Fix SkSwizzler bug

Now, that we are subsetting, fX0 is not necessarily less than
fSrcWidth (since fSrcWidth is really the subset width).

Ex: We may want a 10 pixel subset starting twenty pixels from the
left edge.  In that case, fX0=20 and fSrcWidth=10.

Let's rename the width as fSubsetWidth to avoid confusion
and remove the check.

BUG=skia:

Review URL: https://codereview.chromium.org/1407603003

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/CodexTest.cpp b/tests/CodexTest.cpp
index 91fb6897b5..5ef1f8a86e 100644
--- a/tests/CodexTest.cpp
+++ b/tests/CodexTest.cpp
@@ -220,6 +220,26 @@ static void check(skiatest::Reporter* r,
                 == 0);
         REPORTER_ASSERT(r, codec->skipScanlines(1)
                 == 0);
+
+        // Test partial scanline decodes
+        if (supports_scaled_codec(path) && info.width() >= 3) {
+            SkCodec::Options options;
+            int width = info.width();
+            int height = info.height();
+            SkIRect subset = SkIRect::MakeXYWH(2 * (width / 3), 0, width / 3, height);
+            options.fSubset = ⊂
+
+            const SkCodec::Result partialStartResult = codec->startScanlineDecode(info, &options,
+                    nullptr, nullptr);
+            REPORTER_ASSERT(r, partialStartResult == SkCodec::kSuccess);
+
+            for (int y = 0; y < height; y++) {
+                const int lines = codec->getScanlines(bm.getAddr(0, y), 1, 0);
+                if (!isIncomplete) {
+                    REPORTER_ASSERT(r, 1 == lines);
+                }
+            }
+        }
     } else {
         REPORTER_ASSERT(r, startResult == SkCodec::kUnimplemented);
     }